DVD Durability Issues

I make short films for local elementary schools and put them on DVD's. Lately, the DVD's have been giving me issues. While playing them DVD's on the players (Samsungs and Sanyos), they play well the first few times. However, after awhile, they begin to skip and eventually become unreadeable.

My setup:

Sony VAIO
DVD Architect 3
HP DVD Burner
Mermorex DVDs

Furthermore, DVDs that I play a lot during short time periods (3 seperate times in 30 minutes) are the ones that become undreadable more so than long time periods (3 seperate times in 3 months).

-the quality of the media (try a different brand - genuine Tayo Yuden has gotten good reviews)
-the quality of the burn (don't burn at the highest burn speed -- try 4x or lower)
-the burner -- check if there's a burner firmware update available (follow instructions when updating firmware)
-the quality of the burning software -- I use DVDDecryptor to burn -- so far it's been great (they updated the burning engine as a separate burning tool since Decryptor is no longer updated))...
-the handling of the discs (don't touch the surface, handle by outer edges)
-whether or not you put a sticky label on the disc (you should not)